We just learned about a car's Muffler
Inside a car engine, when the pistons go up to push on the gas and make it ready to explode, the spark plug is the thing that lets out a little spark like a match lighting a fire, and BOOM the gas explodes and pushes the piston back down.
(From: Wikipedia - spark plug)
The spark plug gets it's electricity from the car's battery, which looks like a big square block.
(From: Wikipedia - lead acid battery)